1. Field of the Invention
This invention relates to an expansion valve and a refrigerating system for use in an air conditioner of a car, refrigerating display case, or the like.
2. Description of the Prior Art
FIG. 6 shows a cooling cycle of an air conditioner of a car. The cooling cycle 50 comprises a compressor 51 driven by an engine (not shown) via a clutch, condenser 52 for cooling and condensing a gaseous refrigerant heated and compressed by the compressor 51, liquid tank 53 for separating the refrigerant condensed by the condenser 52 into vapor and liquid and for removing moisture and dust from the refrigerant, expansion valve 54 for expanding the refrigerant from the liquid tank 53, and evaporator 55 for heat-exchange between air and the refrigerant to cool the air to be blown into the compartment, which all are connected by a pipe network.
Typically used as the expansion valve 54 in the refrigerating cycle is one of an internal pressure-equalizing type disclosed by Japanese Patent Laid-Open Publication Sho 51-86852, which includes a pressurizing chamber and a pressure-equalizing chamber which are separated into upper and lower divisions by a diaphragm, the pressure-equalizing chamber being communicated with the inner space of the main body through a pressure-equalizing path.
R11 (CCl.sub.3 F), R12 (CCl.sub.2 F.sub.2) and other conventional flongroup materials had been used as refrigerants for cooling or refrigerating systems of the type referred to above. However, these materials in which all hydrogen atoms of hydrocarbon radicals have been replaced by chlorine-containing halogen are subject to a worldwide restraint to stop the destruction of the ozone layer in the stratosphere. To provide alternate flon-group refrigerants that will not destruct the ozone layer, hydrogen-containing halogenated hydrocarbon refrigerants, such as R22 (CHClF.sub.2), R123 (CF.sub.3 CHCl.sub.2), R111b (CCl.sub.2 FCH.sub.3), R131a (CF.sub.3 CH.sub.2 F), and R152a (COOF.sub.2 CH.sub.3), have been developed. Among them, non-chlorinated halogenated hydrocarbon, such as R134a (CF.sub.3 CH.sub.2 F) and R152a (CHF.sub.2 CH.sub.3), are considered hopeful.
Non-chlorinated halogenated hydrocarbon, however, is inferior to conventional flon-group refrigerants in respect of lubricity, and often causes metallic powder to mix in the refrigerant.
Since the expansion valve, among various elements of a refrigerating cycle, comprises a valve member opening and shutting an orifice, the valve seat of the orifice is subject to local abrasion or a sort of corrosion called erosion by metallic powder or other particles contained in the refrigerant.
Japanese Patent Laid-Open Publication Hei 5-346276 discloses a construction in which a guide member made of SUS is slidably disposed in an orifice portion of a valve body made of brass to guide an actuating rod for operating the valve.